Calling LogonUser with account that has autogenerated password

The MSFT doc states out of the box that aspnet_wp runs under the
installed account ASPNET. However this account has an autogenerated
password. I assuming they are using the LogonUser function to get a
handle to the this user, and from here do something like
create_process_as_user.

If these assumptions are correct how are they logging in under this
account if they don't know the password? My thinking maybe way off.

I was trying to write some test code that required to be running under
ASPNET and I did not want to do this inside an asp.net page (using a
testing framework).

Thoughts
Don

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